The long term objective of this proposal is to develop reagents that will indicate the extent of, or may intervene in the transformation of human lymphocytes infected by retroviruses. Unlike other studies and findings that deal directly with retroviruses and their products, in this Phase I proposal we will study a specific response of lymphocytes to retroviral transformation. The proposed studies are based on our recent findings that human T-cell lines normally express a 5.5 kb MRNA that codes for the receptor for the mitogenic form of the platelet-derived growth factor (PDGF-BB). This receptor (PDGFR-B) is localized on the cell surface. However, HTLV-I-infected T-cell lines express only a 4.8 kb PDGFR-B MRNA that codes for a protein that is localized intracellularly. We have also detected an identical 4.8 kb PDGFR-B MRNA in one HIV-infected T-cell line tested, but only the 5.5 kb MRNA species in B-lymphocytic lines infected with the DNA-virus, Epstein-Barr (EBV). We propose to monitor changes in the size of PDGFR-B MRNA in lymphocytes before and after retrovirus-infection (Aim 1). Further, we will identify and subcellularly localize the PDGFR-B protein (Aim 2). Expression of PDGFR-B mRNAs will be detected by Northern hybridization analysis using a specific PDGFR-B CDNA probe. The presence and molecular size of PDGFR-B protein. in infected cells will be detected by indirect immunofluorescence and radioimmunoprecipitation using a polyclonal antibody raised against a synthetic peptide corresponding to a specific region of the human PDGFR-B. The results of these studies (Phase 1) will indicate whether human lymphocyte transformation by retroviruses correlates with the expression of aberrant PDGFR-B mRNAs of different sizes and consequently different PDGFR- B proteins.